The present invention relates to a digital-to-analog converter DA converter which converts a digital signal into an analog signal of a corresponding magnitude and, more particularly, to a pulse width modulated (PWM)-type DA converter having an improved conversion speed and which is capable of effectively attenuating the ripple components of the PWM waves.
According to a general PWM-type DA converter, an input digital signal to be converted is compared with a reference digital signal which changes in magnitude within one period. Based on the comparison result obtained, a pulse signal PWM wave, having a of the pulse width corresponding to the magnitude of the input digital signal is generated. This PWM wave is smoothed to obtain an output analog signal. A DA converter of this type has an advantage in that the conversion precision can be easily improved by increasing the number of bits of the reference digital signal. The PWM-type DA converter is, therefore, widely adopted especially in servo control of motors since it is easily integrated. However, the pWM-type DA converter also has disadvantages. For example, the output analog signal is determined only one period after the reference digital signal. Since the input signal is passed through a low-pass filter for the purpose of smoothing, the conversion speed is slower than that obtainable with DA converters of other types. Furthermore, the smoothing is insufficient and the ripple components tend to be included in the output signal.